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Mon, 09 Sep 2024 06:14:51 -0700 (PDT) From: Celeste Liu X-Google-Original-From: Celeste Liu Message-ID: Date: Mon, 9 Sep 2024 21:14:43 +0800 Precedence: bulk X-Mailing-List: linux-tegra@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/4] riscv: defconfig: drop RT_GROUP_SCHED=y Content-Language: en-GB-large To: Conor Dooley Cc: Paul Walmsley , Palmer Dabbelt , Albert Ou , Guo Ren , Anup Patel , Heinrich Schuchardt , Huacai Chen , WANG Xuerui , Yoshinori Sato , Rich Felker , John Paul Adrian Glaubitz , Russell King , Florian Fainelli , Broadcom internal kernel review list , Ray Jui , Scott Branden , Tony Lindgren , Thierry Reding , Jonathan Hunter , Palmer Dabbelt , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, loongarch@lists.linux.dev, linux-sh@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-rpi-kernel@lists.infradead.org, linux-omap@vger.kernel.org, linux-tegra@vger.kernel.org References: <20240823-fix-riscv-rt_group_sched-v2-0-e4dbae24f7e1@gmail.com> <20240823-fix-riscv-rt_group_sched-v2-1-e4dbae24f7e1@gmail.com> <20240909-gave-celtic-af2ea8bc38d5@wendy> <9e364ae4-dc2c-4efa-8611-462218402a5d@gmail.com> <20240909-arguable-detection-02445bd1cc89@wendy> In-Reply-To: <20240909-arguable-detection-02445bd1cc89@wendy> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 2024-09-09 21:06, Conor Dooley wrote: > On Mon, Sep 09, 2024 at 08:14:16PM +0800, Celeste Liu wrote: >> On 2024-09-09 19:53, Conor Dooley wrote: >> >>> On Fri, Aug 23, 2024 at 01:43:26AM +0800, Celeste Liu wrote: >>>> Commit ba6cfef057e1 ("riscv: enable Docker requirements in defconfig") >>>> introduced it because of Docker, but Docker has removed this requirement >>>> since [1] (2023-04-19). >>>> >>>> For cgroup v1, if turned on, and there's any cgroup in the "cpu" hierarchy it >>>> needs an RT budget assigned, otherwise the processes in it will not be able to >>>> get RT at all. The problem with RT group scheduling is that it requires the >>>> budget assigned but there's no way we could assign a default budget, since the >>>> values to assign are both upper and lower time limits, are absolute, and need to >>>> be sum up to < 1 for each individal cgroup. That means we cannot really come up >>>> with values that would work by default in the general case.[2] >>>> >>>> For cgroup v2, it's almost unusable as well. If it turned on, the cpu controller >>>> can only be enabled when all RT processes are in the root cgroup. But it will >>>> lose the benefits of cgroup v2 if all RT process were placed in the same cgroup. >>>> >>>> Red Hat, Gentoo, Arch Linux and Debian all disable it. systemd also doesn't >>>> support it.[3] >>>> >>>> [1]: https://github.com/moby/moby/commit/005150ed69c540fb0b5323e0f2208608c1204536 >>>> [2]: https://bugzilla.redhat.com/show_bug.cgi?id=1229700 >>>> [3]: https://github.com/systemd/systemd/issues/13781#issuecomment-549164383 >>>> >>>> Fixes: ba6cfef057e1 ("riscv: enable Docker requirements in defconfig") >>> >>> I don't think this fixes tag is suitable, the commit you cite in >>> moby/docker is a year younger than the one in the fixes tag, so it was >>> correct at the time it was written. I think the fixes tag should just be >>> removed, since that commit was not wrong. Or am I missing something? >> >> The Docker commit I cited introduce the fix, not the bug. So it should be later >> than commit in fixes tag, otherwise Heinrich Schuchardt won't pick the wrong >> config from upstream. >> >> Timeline is: >> 1) 2015-06-19 Qiang Huang introduce RT_GROUP_SCHED check in Docker.[1] >> 2) 2022-06-08 Heinrich Schuchardt pick this to defconfig in commit >> in fixes tag. >> 3) 2023-04-19 Florian Schmaus remove this requirement from Docker in >> commit I cited. > > Yes, this is the way I understood things to be. IOW, when Heinrich wrote > ba6cfef057e1 ("riscv: enable Docker requirements in defconfig"), it was > a requirement for docker. The requirement later being removed doesn't > make his patch incorrect, which is why I don't think this is a fix. Oh, you are right. I will send v3 later.